A 50-year-old man with a troubled past who earned the nicknames "Bad Elmo" and "Evil Elmo" for donning a furry red costume and posing for pictures with tourists - while sometimes assailing them with obscene, anti-Semitic rants - has been working Fisherman's Wharf in recent weeks.

There, Dan Sandler has run into a different sort of tension, one centered on his notoriety and local street kids' desire to execute what they describe as "street justice."

Since he began mugging for photos in front of a candy store a few weeks ago, a small group of transients have been trying to harass him away. The scuffles they've started have alarmed merchants, who say they were already sufficiently alarmed by the presence of a giant "Sesame Street" character played by a man who once ran a website in Cambodia titled "Welcome to Rape Camp."

"Even though he's never been convicted, people see him as a child molester who is trying to target children - he stands outside of a candy store in an Elmo costume," said Troy Campbell, the executive director of the Fisherman's Wharf Community Benefits District. "Just knowing his history, you want to grab and warn every parent, but you can't do that."

Sandler's saga - which has played out prominently on the Internet - has been long, lurid and portable.

First, he was New York's problem, after he got into it with tourists while aggressively asking for money in Central Park and Times Square. He was taken into custody multiple times, and once convicted for disorderly conduct.

Then he was San Francisco's problem, then Los Angeles' problem, then Honolulu's problem. He became New York's problem again in May, when San Francisco police booked him on a warrant and sent him back to Manhattan to face charges of trying to extort $2 million from the Girl Scouts of America.

As it turned out, Sandler - who couldn't be reached for this story - had even stranger episodes in his past.

Before he discovered that dressing as Elmo was a good way to scare up tourist tips, he spent time in Cambodia in the 1990s operating the pornography site, until he was deported.

In San Francisco, Sandler has mostly been sighted on the weekends, posing for pictures in front of the It'Sugar candy store on Jefferson Street. A store manager said she could not comment without corporate approval, but staffers - all young women - said they were uncomfortable with him in front of the store.

"There's just something very off-putting about him," said Randy Salazar, 23, who works at Crazy Shirts on the same block. Salazar did not know Sandler's history in detail, but said he "gave off bad vibes."

Parents have reported an Elmo behaving in similar fashion in San Francisco in October 2012, yelling anti-Semitic obscenities at Rossi Park in the Inner Richmond neighborhood. Parents there told The Chronicle the man appeared to be Sandler.

Capt. Garrett Tom, who heads Central Station, said not much has changed this time around: Sandler was cited by officers Sunday at Fisherman's Wharf for aggressive panhandling.

A beat officer, Tom said, observed Elmo asking a family for money after they took a photo with him in front of the candy store. When they refused to pony up, Sandler followed them, Tom said.

That same day, altercations broke out between Elmo and the self-identified street kids, who are teenagers and young men.

"Four suspects - three males and a female - approached him, started calling him a child molester, yelling at passersby to keep their kids away from him," Tom said. "Sandler said he didn't know who these people were and that one of the males pulled out a pocket knife and started to threaten him."

The encounter spooked a group of tourists, who fled. The four suspects left before police arrived, Tom said.

Later, another street kid stood next to Elmo holding a sign reading, "Rape-O." The young man was taken in for a psychiatric evaluation, Tom said.

On Monday, a person who asked to be identified only as "Jason" proudly owned up to being the sign-holder.

"I got arrested because of him," he exclaimed. "I told the cops that if I knew I wouldn't get in trouble, I'd beat the crap out of him."

A friend added, "I hope some day that man catches on fire."

The street kids are aware of the limitations police face with Sandler. There's not much officers can do unless they witness Elmo breaking the law by aggressively panhandling or harassing passersby.

"If he commits a crime, then we can always go to the district attorney's office and ask for a stay-away order," Tom said. "But it has to be more than aggressive panhandling. It has to be numerous times or something a little more serious."

Jason said he believes it's up to the street kids.

"There's justice, then there's street justice," he said. "It's up to the street kids to take care of the things the police can't."